Mercury Jet 120

[mitko]

In October of 2004 I bought a jet boat '95 SEARAY F14.The boat spent the winter outdoors and when I tried to test in on water,few weeks ago, I ran into some serious problems.I succesfully started the motor and it ran for about 2-3 minutes and then went dead. The motor seemed to be like blocked after that. After an hour, when the system was cooled down, I was able to start again,but with the same result.Also when I started the motor out of the water there was mixed gas and oil leacking under the jet drive.<br />Please help! Any thought will be appreciated.

 

[kenimpzoom]

Re: Mercury Jet 120

Describe "blocked". Does that mean the engine would not turn over at all, or that the eninge just would not start.<br /><br />How much gas and oil was leaking under the jet drive.<br /><br />Dont start the eninge out of the water unless you have the proper water supply.<br /><br />If you have raw fuel from under the jet drive, something is seriouusly wrong with the carbs, perhaps the floats are stuck open.<br /><br />Ken

 

[mitko]

Re: Mercury Jet 120

Hi Ken, when I tried to restart the motor it's look that the starter don't have power to spin the motor. The starter is new.<br />It's hard to say how much gas and oil is leaking because the water, but I will say just enough to color the water.<br />Thanks.

 

[trpaddy]

Re: Mercury Jet 120

Mitco, pull your plugs, ground them, then spin your motor, any unusual liquids comming out of your cylinders?

 

[mitko]

Re: Mercury Jet 120

I have some fuel from the top two plugs, and the 8 inch line between the carbs was full whit dirt. I remuved the plastic cover from the carbs and some fuel start licking from the bottom carb.

 

[kenimpzoom]

Re: Mercury Jet 120

If fuel is leaking from the carb, it has a stuck float. Try tapping gently on the carb to let the flat come down. <br /><br />You probably need to rebuild the carbs.<br /><br />You need to do a compression check also.<br /><br />When you say the engine ran for 2-3 minutes was that a idle, or was that while going fast?<br /><br />You may have a cooling problem which heats up the engine, then it gets really hard to spin. When it cools down, it will spin easy again.<br /><br />Like I said, you need to do a compression check.<br /><br />Actually, step one is to buy the proper manual.<br /><br />Ken

 

[mitko]

Re: Mercury Jet 120

Hi Ken, I do have manual but can't find anyting about cooling sistem, I guess this motor don't have water pump. The engine ran for 2-3 minutes on idle.<br />I will rebuild the carbs this saturday hope will help.<br />Thanks

 

[kenimpzoom]

Re: Mercury Jet 120

The cooling water comes from the jet, there is no water pump.<br /><br />Look at the engine from the top in the back (where the spark plugs are). You should see a rubber hose coming from the base going up into the engine.<br /><br />There should be some mention of cooling, what brand manual do you have?<br /><br />The next time you start it, and it quits, see how hot the engine is. If you can keep you hand on the head you are OK.<br /><br />Also, I suggest you rebuild the fuel pump at the same time, it is easy.<br /><br />Ken

 

[mitko]

Re: Mercury Jet 120

Hi Ken, I have Clymer Mercury Sport Jet shop manual.<br />I am using a Dealer Flushing Adaptor to run the motor in my garage. When the motor stop I put my hand on the engine and it was hot but not that I can't keep my hand oh it, so I will say it's not overheated. Last test /today/ the motor did't stop, but after 5-6 min. the overheat alarm sound, I can keep my hand on the motor. I guess it's the carbs, but I will check the fuel pump too.<br />Thanks again.<br />Mitko

 

[kenimpzoom]

Re: Mercury Jet 120

If you are using the dealer flushing adaptor, it should not overheat, and the overheat alarm should not sound.<br /><br />Something is wrong with your cooling.<br /><br />Are you certain you have the water on fast enough. I turn it on about halfway. A pretty fast flow comes out the bottom of the jet (engine running or not). Are you getting good flow?<br /><br />I have heard of people getting sand/debris in the motor and hose, you may want to check that you hose isnt blocked.<br /><br />Check page 71 of your manual for more info.<br /><br />Ken

 

[mitko]

Re: Mercury Jet 120

I am not shure that the water presure is enough, I have the water from the botom of the boat but not fast, maybe I need more preshure.<br />Thanks

 

[funpilot]

Re: Mercury Jet 120

By dealer flushing adapter, I hope you mean you are disconnecting the hose at the rear of the engine between the jet pump and engine and connecting an adaptor which allows you to connect a garden hose directly. Under normal use, the jet pump supplies water, via a bypass of the water flowing through the impeller. Any other method won't provide enough flow to run the engine.<br /><br />You need to run enough water pressure to make a pretty good mess. The water also carries away unburned fuel and gasses from the exhaust, so you have to start the water before you start the engine, or you can backfire and blow off the ride plate. The thermostat rarely fails, but you might have blocked cooling passages. The jet pump is a great vacuum cleaner, it will suck everything off the bottom. At slow or no speeds you need about three feet clear of the bottom for depth. At high speed in shallower water, you can move faster than the boat can suck the bottom up.<br /><br />Another thought is that the oil injection system is not set up right. Too much oil can foul the plugs, too little will cause the rings to bind.<br /><br />But, I'm betting on sticky floats or leaking needle seats.<br /><br />Good luck,<br />fp

 

[mitko]

Re: Mercury Jet 120

Hi guys, I am using dealer adaptor and when start the water first can't start the motor, so remuve the sparks start the motor and got water from he bottom cilinder. If I start the motor first and water second it's work fine.

 

[funpilot]

Re: Mercury Jet 120

Mitko,<br /><br />Sometimes the water can get into the motor from the dealer flushing adapter. It happens when the bottom cylinder is in an exhaust position, and the water pressure is too high. Either assure the cylinder is covering the exhaust port or I think a better idea would be to start the water at a low rate of flow, see if the engine will start, and then increase the flow once you have the engine started.